With the rapid industrial development, rapid population increase and other worldwide problems, water pollution is aggravated and water resource is in short. In recent years, 60 billion cubic meters of industrial wastewater and 20 billion cubic meters of domestic sewage are discharged each year in China. The seven major water systems, such as the Yangtze River and the Yellow River, are seriously polluted. The quality of water in ecological lakes and offshore regions is deteriorated to different extents. People's health and economic development are seriously threatened. The protection of water resource is highly urgent. China is one of the countries which are urgently lack of water, and its per-capita fresh water resource is only ¼ of the world average. Due to a large population and with the social development, the large amount of produced industrial wastewater and domestic swage seriously pollutes the limited water resource. Some phenomena of water shortage are shocking, and water resource has been at risk. The Water Law of the People's Republic of China established laws such as water resource protection, water conservation and efficient water use from the perspective of legislation. Water has become the scarcest resource.
For decades, during the sustainable utilization of water resource which maintains the human society, economic development and living environment, chemical flocculants play a significant role in purification of surface water and sewage treatment. However, by scientific research, it is increasingly found that chemical flocculants have chemical toxicity and contain hardly-degradable substance, and the residue and accumulation of chemical flocculants after being used and the migration and transformation thereof will cause serious harm to the human health, biodiversity interference and ecosystem balance.
Microbial flocculants are natural biological macromolecules produced by microorganisms, and are environmentally friendly products due to their properties of mild production conditions, non-toxic and harmless essence, high-efficiency, and environmental biodegradability. Microbial flocculants are novel biological water treatment agents, belonging to the modern novel fermentation products. The research on microbial flocculants has become the hot issue of the academic circles all over the world, and the science orientation has enabled microbial flocculants to be highly demanded. In the Twelfth Five-Year Plan of Biological Industry Development issued by the State Council in 2013, the industrialization and the popularization and application of novel fermentation products, and the development of high-performance environmentally friendly biological agents have already been taken as the key developing fields. However, in view of the research situation of microbial flocculants in the past 30 years, poor performance of spawn, costly production substrate, less-reasonable fermentation process, low product activity and similar problems still remain, resulting in low production output, high production cost and high product price. Consequently, the feasibility of specialization and the market acceptability are influenced.
For more than a decade, LUAN, Xingshe, the inventor of the present invention patent application, has been working on the research and development of microbial flocculants, and have achieved two patents: ZL200310105515.X and ZL201210010801.7. In ZL200310105515.X (inventor: LUAN, Xingshe; title: METHOD FOR PREPARING BIOFLOCCULANTS FROM ARTHROBACTER), the inventor selected arthrobacter for producing microbial flocculants by soil sampling. The metabolism of the selective culture medium for selecting this arthrobacter is highly targeted, and producing the culture medium of biological flocculants by fermentation with this arthrobacter is cheap. However, when producing microbial flocculants by fermentation with this selected strains, the yield is low (≤42%) and the production output is also low (≤0.9%). In ZL201210010801.7 (inventor: LUAN, Xingshe; title: METHOD FOR PREPARING BIOFLOCCULANTS BY HIGH-CONCENTRATION FERMENTATION), the inventor achieved higher production output (≥2.0%) by fermentation in a bacterial quantity dominance way by separated micrococcus DS16. However, this method increases the equipment investment, and both the fermentation process and operation steps are slightly complex. Hence, for microbial flocculants which are green environmentally-friendly biological agents, making further improvements, maintaining the high efficiency, making the process more scientific and reasonable, increasing the production output and yield, and reducing the production and use cost are technical difficulties which must be overcome before the industrialization and the popularization and application.